1. Field of the Invention
The present invention relates to planarization and polishing of substrates in a substrate processing system. More specifically, the present invention relates to methods and apparatus for cleaning a pad in a planarization and polishing system.
2. Description of the Related Art
Integrated circuits are typically formed on substrates, particularly silicon wafers, by the sequential deposition of conductive, semi-conductive or insulative layers. After each layer is deposited, the layer is etched to create circuitry features. As a series of layers are sequentially deposited and etched, the uppermost surface of the substrate may become non-planar across the substrate surface and require planarization. The non-planarity occurs when the thickness of the layers formed on the substrate varies across the substrate surface as a result of the non-uniform geometry of the circuits formed thereon.
Chemical mechanical polishing (CMP) is one accepted method of planarization. In CMP, a substrate is typically placed face down on a polishing pad located on a large rotatable platen. The polishing pad can be a removable pad attached to the platen for a useful life of the pad and then replaced. Alternatively, the pad can be a sheet of polishing material that is incrementally indexed across a rectangularly shaped platen as the material wears. This type of system is conventionally known as a xe2x80x9cwebxe2x80x9d system. A carrier holds the substrate and applies pressure to the back of the substrate to hold the substrate against the polishing pad during polishing.
In a slurry-based system, a mixture of abrasives and chemicals is delivered to the polishing pad to chemically passivate or oxidize the film being polished and abrasively remove or polish off the surface of the film. A reactive agent in the slurry reacts with the film on the surface of the substrate to facilitate polishing. The interaction of the polishing pad, the abrasive particles, and the reactive agent with the surface of the substrate results in controlled polishing of the desired film.
However, the slurry delivered to the polishing pad can coagulate with the material being removed from the substrate and clog the grooves or pore structure on the pad, thereby reducing the effectiveness of the planarization process and increasing the likelihood of poor planarization performance. Further, the polishing process creates debris on the pad that can scratch the substrate during subsequent polishing. Additionally, in a web polisher, corners of rectangular polishing sheets that do not initially engage the substrate are susceptible to clogging with debris from a central area that does engage the substrate. When the sheet of polishing pad material is indexed so that the material that was at the corners is moved to a position to polish the substrate, the coagulated debris can cause scratches and defects in the substrate during polishing. Thus, it is important to thoroughly clean the debris from the pad.
As another example of polishing pads that need debris removal, recent efforts in the field of substrate processing have developed a planarization system using a polishing pad known as a fixed abrasive pad that does not require a slurry. The fixed abrasive pad includes a plurality of microscopic pedestals that abrade the substrate in the planarization process. However, the debris generated from pad asperity may scratch the substrate, thereby requiring replacement or cleaning of the pad.
Prior efforts at cleaning slurry-based polishing pads, such as brushing the debris, are not effective in removing debris lodged between the pedestals on a fixed abrasive pad. Generally, the size of brush bristles is larger than the spacing between the pedestals and therefore do not provide effective cleaning between the pedestals. Another technique which has been used to clean polishing pads is xe2x80x9chigh pressurexe2x80x9d de-ionized water rinse. However, heretofore the xe2x80x9chigh pressurexe2x80x9d deionized water is delivered to the pad directly downward or at too low a pressure at the nozzle and the rinse does not remove or sweep debris from the pad.
Therefore, there remains a need for a system and method for cleaning polishing pads in a substrate processing system and particularly for cleaning fixed abrasive pads.
The present invention generally provides a system and apparatus for cleaning a polishing pad, such as a fixed abrasive pad, in a substrate processing system. In one embodiment, the system includes one or more nozzles which spray a fluid at pressures of about 30 psi to about 300 psi or greater, as measured at the nozzle, onto a polishing pad at acute angles to the surface of the polishing pad. The nozzles can spray downward and outward toward the perimeter of the pad to facilitate the debris removal therefrom. The system can include a pressure source to produce a sufficient fluid pressure substantially higher than the typical fluid pressure available from a facility installation.
In one aspect, the invention provides an apparatus for polishing a substrate, comprising a rinse fluid rinse arm disposed above the polishing pad, and one or more nozzles coupled to the rinse arm and mounted to spray the rinse fluid at an acute angle to the polishing pad. In another aspect, the invention provides an apparatus for polishing a substrate on a polishing pad, comprising a rinse arm disposed above the polishing pad, and one or more nozzles coupled to the rinse arm that direct a rinse fluid to the polishing pad at a rinse fluid pressure at least about 30 psi to rinse the pad.
In another aspect, the invention provides a system for polishing a substrate on a polishing pad, comprising a rinse arm disposed above the polishing pad, one or more nozzles coupled to the rinse arm, and a vacuum arm disposed above the polishing pad. In another aspect, the invention provides a system for polishing a substrate on a polishing pad, comprising a base, one or more carriers supported above the base, a rinse fluid rinse arm disposed above the polishing pad, and one or more nozzles coupled to the rinse arm and mounted to spray the rinse fluid at an acute angle to the polishing pad.